Comparative phenotypic and transcriptomic analyses reveal the potential molecular basis of forming bigger leaf blade in autotetraploid castor bean

Background Whole-genome duplication events often confer autopolyploid plants with bigger leaf blades compared with those of their diploid counterparts. However, little is known regarding the potential molecular basis of bigger leaf formation in autopolyploid plants. Here, we focused on the oilseed crop castor bean ( Ricinus communis L. ) to investigate the molecular basis underlying leaf size variation using a synthetic autotetraploid by doubling the diploid homologous chromosomes. Results The results showed that the leaf area of autotetraploids was significantly larger than that of diploids. According to our histological observations, the formation of larger leaf blades in tetraploid castor beans is attributed to both an increase in cell size and an increase in cell number. A total of 3,464 differentially expressed genes (DEGs) between diploids and tetraploids were identified by RNA sequencing analysis. The expression of key genes related to cell wall loosening, cell expansion and cell division was higher in tetraploid leaf blades compared to diploids, resulting in enlarged tetraploid leaf blades, such as SUS2 , SUS4 , XYL1 , Xyl2 , XTH30, XTH32, EXPA1 , EXPA4 , EXPA6 , EXPB3 , CYCD3 ; 1 and CYCD3 ; 3 were significantly up-regulated in tetraploids. Moreover, the expression of auxin response genes, including SAUR20 , SAUR23 , and SAUR53 , in the auxin signaling pathway was significantly up-regulated in tetraploids, facilitating leaf cell expansion and ultimately contributing to the enlargement of tetraploid leaf blades. Conclusions Our findings provide important insight into understanding the potential molecular basis of gene dosage effects on trait variation in autopolyploid plants.